U.S. patent number 4,834,735 [Application Number 06/887,584] was granted by the patent office on 1989-05-30 for high density absorbent members having lower density and lower basis weight acquisition zones.
This patent grant is currently assigned to The Proctor & Gamble Company. Invention is credited to Miguel Alemany, Charles J. Berg.
United States Patent |
4,834,735 |
Alemany , et al. |
May 30, 1989 |
**Please see images for:
( Certificate of Correction ) ** |
High density absorbent members having lower density and lower basis
weight acquisition zones
Abstract
An absorbent article wherein the deposition region of its
absorbent member comprises a storage zone and an acquistion zone
having a lower average density and a lower average basis weight per
unit area than the storage zone. The acquisition zone is positioned
toward the front of either the absorbent member or the absorbent
article so that the acquistion zone may most effectively and
efficiently rapidly acquire discharged liquids. The absorbent
member also comprises a mixture of hydrophilic fibrous material and
discrete particles of absorbent gelling material to enhance the
absorbent capacity of the absorbent member.
Inventors: |
Alemany; Miguel (Cincinnati,
OH), Berg; Charles J. (Cincinnati, OH) |
Assignee: |
The Proctor & Gamble
Company (Cincinnati, OH)
|
Family
ID: |
25391451 |
Appl.
No.: |
06/887,584 |
Filed: |
July 18, 1986 |
Current U.S.
Class: |
604/368; 428/913;
428/213; 428/218 |
Current CPC
Class: |
A61F
13/511 (20130101); A61F 13/533 (20130101); A61F
13/53752 (20130101); A61F 2013/530481 (20130101); Y10T
428/2495 (20150115); A61F 2013/1543 (20130101); A61F
2013/530445 (20130101); Y10S 428/913 (20130101); A61F
2013/53051 (20130101); A61F 2013/53795 (20130101); Y10T
428/24992 (20150115); A61F 2013/15422 (20130101); A61F
2013/15406 (20130101) |
Current International
Class: |
A61F
13/15 (20060101); A61F 013/16 () |
Field of
Search: |
;428/283,284,213,218,913
;604/368 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1128704 |
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Aug 1982 |
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CA |
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0062495A2 |
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Oct 1982 |
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EP |
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0158914A2 |
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Oct 1985 |
|
EP |
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2124907A |
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Feb 1984 |
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GB |
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Primary Examiner: Bell; James J.
Attorney, Agent or Firm: Miller; Steven W. Pollaro; John M.
Braun; Fredrick H.
Claims
What is claimed is:
1. An absorbent member having a back section and a front section
contiguous with said back section, said front section having an end
region and a deposition region contiguous with said end region and
said back section so that said deposition region is positioned
between said end region and said back section, the absorbent member
comprising:
a mixture of hydrophilic fibrous material and discrete particles of
absorbent gelling material;
a storage zone positioned in at least said deposition region of the
absorbent member; and
an acquisition zone positioned in at least said deposition region
of the absorbent member, said acquisition zone having a density and
basis weight per unit area greater than zero, said acquisition zone
having a lower average density and a lower average basis weight per
unit area than said storage zone, said storage zone at least
partially laterally surrrounding the perimeter of said acquisition
zone so as to be in liquid communication with at least a portion of
the lateral area of said acquisition zone.
2. The absorbent member of claim 1 wherein said acquisition zone
extends from the top surface of the absorbent member through at
least a fraction of the total thickness of the absorbent member,
the top surface area of said acquisition zone being completely
positioned within said front section.
3. The absorbent member of claim 2 wherein the top surface area of
said acquisition zone comprises less than about 50% of the top
surface area of said front section.
4. The absorbent member of claim 1 wherein said acquisition zone
extends from the top surface of the absorbent member through at
least a fraction of the total thickness of the absorbent member,
the top surface area of said acquisition zone being completely
positioned within said deposition region.
5. The absorbent member of claim 4 wherein the top surface area of
said acquisition zone comprises less than about 50% of the top
surface area of said front section.
6. The absorbent member of claim 4 wherein the top surface area of
said acquisition zone comprises less than about 35% of the top
surface area of said front section.
7. The absorbent member of claim 4 wherein the top surface area of
said acquisition zone comprises less than about 20% of the top
surface area of said front section.
8. The absorbent member of claim 7 wherein said acquisition zone is
positioned so that at least 30% of the top surface area of said
acquisition zone is positioned in the front half of said front
portion.
9. The absorbent member of claim 5 wherein said acquisition zone
has a thickness approximately equal to the thickness of said
storage zone.
10. The absorbent member of claim 9 wherein said back section has a
thickness approximately equal to the thickness of said deposition
region.
11. The absorbent member of claim 10 wherein said end region has a
thickness approximately equal to the thickness of said deposition
region.
12. The absorbent member of claim 11 wherein said acquisition zone
extends through the entire thickness of the absorbent member.
13. The absorbent member of claim 12 wherein the top surface area
of said acquisition zone is transversely centered within said
deposition region.
14. The absorbent member of claim 13 wherein the top surface area
of said acquisition zone has a generally triangular shape.
15. The absorbent member of claim 9 wherein said deposition region
has a thickness greater than an about 1.5 times the thickness of
said back section.
16. The absorbent member of claim 9 wherein said deposition region
has a thickness greater than about 2.0 times the thickness of said
back section.
17. The absorbent member of claim 16 wherein the top surface area
of said acquisition zone is transversely centered within said
deposition region.
18. The absorbent member of claim 17 wherein the top surface area
of said acquisition zone has an oval shape.
19. The absorbent member of claim 9 wherein said front section
further has two transversely spaced ear regions and a central
region disposed intermediate said ear regions, said acquisition
zone being positioned within said central region.
20. The absorbent member of claim 19 wherein said ear regions have
a thickness substantially less than the thickness of said central
region of said front portion.
21. The absorbent member of claim 20 wherein said ear regions and
said central regions are demarked from each other by sufficiently
abrupt thickness differences that said front section has a terraced
character.
22. The absorbent member of claim 20 wherein said ear regions have
a greater average density than said storage zone positioned within
said central region.
23. The absorbent member of claim 13 wherein the top surface area
of said acquisition zone has a funnel shape.
24. The absorbent member of claim 13 wherein the absorbent member
has an asymmetrical shape.
25. The absorbent member of claim 24 wherein the average density of
said back section is less than the average density of said storage
zone of said deposition region.
26. The absorbent member of claim 25 wherein the top surface area
of said acquisition zone has a generally triangular shape.
27. The absorbent member of claim 1 wherein the ratio of the
average density of said storage zone to the average density of said
acquisition zone is about equal to or greater than 1.25:1.
28. The absorbent member of claim 1 wherein the ratio of the
average density of said storage zone to the average density of said
acquisition zone is about equal to or greater than 2:1.
29. The absorbent member of claim 28 wherein the density of said
acquisition zone is from about 0.05 to about 0.15
grams/cm.sup.3.
30. The absorbent member of claim 29 wherein said acquisition zone
has a substantially uniform density and uniform basis weight
throughout.
31. The absorbent member of claim 1 wherein only said deposition
region has discrete particles of absorbent gelling material
dispersed therein.
32. The absorbent member of claim 1 wherein said mixture of
hydrophilic fibrous material and discrete particles of absorbent
gelling material has a fiber-to-particulate weight ratio of from
about 40:60 to about 98:2.
33. The absorbent member of claim 1 wherein said mixture of
hydrophilic fibrous material and discrete particles of absorbent
gelling material has a fiber-to-particulate weight ratio of from
about 50:50 to about 91:9.
34. The absorbent member of claim 33 wherein said particles of
absorbent gelling material have a gel strength such that said
particles have a shear modulus of at least about 2000
dynes/cm.sup.2.
35. The absorbent member of claim 33 wherein said hydrophilic
fibrous material and said discrete particles of absorbent gelling
material are uniformally dispersed with respect to each other
throughout the absorbent member.
36. An absorbent article comprising:
a liquid pervious topsheet;
a liquid impervious backsheet associated with said topsheet;
and
an absorbent member according to claims 1, 2, 4, 9, 12, 16, 18, or
24 positioned between said topsheet and said backsheet.
37. An absorbent member having a back section and a front section
contiguous with said back section, said front section having an end
region and a deposition region contiguous with said end region and
said back section so that said deposition region is positioned
between said end region and said back section, the absorbent member
comprising:
a mixture of hydrophilic fibrous material and discrete particles of
absorbent gelling material;
a storage zone positioned in at least said deposition region of the
absorbent member; and
an acquisition zone positioned in at least said deposition region
of the absorbent member, said acquisition zone having a larger
average pore size of the fibers than said storage zone, said
storage zone at least partially laterally surrounding the perimeter
of said acquisition zone so as to be in liquid communication with
at least a portion of the lateral area of said acquisition
zone.
38. An absorbent article having a front waistband region, a back
waistband region, and a crotch region disposed between said front
waistband region and said back waistband region, said absorbent
article comprising:
a liquid pervious topsheet;
a liquid impervious backsheet associated with said topsheet;
and
an absorbent member positioned between said topsheet and said
backsheet, said absorbent member comprising a mixture of
hydrophilic fibrous material and discrete particles of absorbent
gelling material; a storage zone positioned in at least said crotch
region of said absorbent article; and an acquisition zone
positioned in at least said crotch region of said absorbent
article, said acquisition zone having a density of from about 0.05
g/cm.sup.3 to about 0.41 g/cm.sup.3, said acquisition zone having a
lower average density and a lower average basis weight per unit
area than said storage zone, said acquisition zone extending from
the top surface of the absorbent member through at least a fraction
of the total thickness of the absorbent member, the top surface
area of said acquisition zone comprising less than about 35% of the
top surface area of said absorbent member, said storage zone
laterally surrounding the perimeter of said acquisition zone so as
to be in liquid communication with the lateral area of said
acquisition zone.
39. The absorbent article of claim 38 wherein said absorbent member
has a uniform thickness and said acquisition zone extends through
the entire thickness of said absorbent member.
40. The absorbent article of claim 39 additionally comprising an
absorbent acquisition core positioned between said topsheet and
said absorbent member.
41. The absorbent article of claim 40 wherein said absorbent member
is generally oblong and has a top surface area that is from about
0.25 to about 1.0 times that of said absorbent acquisition core,
said absorbent member being positioned relative to said backsheet
and said absorbent acquisition core in a manner such that at least
75% of the absorbent gelling material in said absorbent member is
found within the front two-thirds portion of the absorbent
article.
42. The absorbent article of claims 38, 40, or 41 wherein said
acquisition zone is positioned relative to said backsheet such that
the top surface area of said acquisition zone is completely
positioned within the front two-thirds section of the absorbent
article.
43. The absorbent article of claim 41 wherein said acquisition zone
is positioned relative to said backsheet such that the top surface
area of said acquisition zone is completely positioned within the
front one-half section of the absorbent article.
44. The absorbent article of claim 43 wherein the top surface area
of said acquisition zone is completely positioned within said
crotch region.
45. The absorbent article of claim 41 wherein said absorbent
acquisition core has a core acquisition zone having a lower average
density and a lower average basis weight than the remainder of said
absorbent acquisition core.
46. The absorbent article of claim 45 wherein said core acquisition
zone of said absorbent acquisition core overlays at least a portion
of said acquisition zone of said absorbent member.
47. The absorbent article of claim 46 wherein said absorbent
acquisition core contains particles of absorbent gelling material
in an amount up to about 50% by weight of said absorbent
acquisition core.
48. An absorbent core comprising:
an absorbent member comprising a mixture of hydrophilic fibrous
material and discrete particles of absorbent gelling material, a
storage zone, and an acquisition zone having a lower average
density and a lower average basis weight per unit area than said
storage zone, said acquisition zone having a density of from about
0.05 to about 0.41 g/cm.sup.3, said storage zone at least partially
laterally surrounding the perimeter of said acquisition zone so as
to be in liquid communication with at least a portion of the
lateral area of said acquisition zone; and
an absorbent acquisition core positioned adjacent said absorbent
member, said absorbent acquisition core comprising hydrophilic
fibers that are substantially free of absorbent gelling material,
said absorbent acquisition core having a core acquisition zone
having a lower average density and a lower average basis weight per
unit area than the remainder of said absorbent acquisition core,
said core acquisition zone being positioned with respect to said
acquisition zone of said absorbent member so as to provide an
overall acquisition zone throughout the entire thickness of the
absorbent core.
49. The absorbent core of claim 48 wherein said core acquisition
zone has the same shape as said acquisition zone of said absorbent
member.
50. The absorbent core of claims 48 or 49 wherein said absorbent
member and said absorbent acquisition core are a continuous web of
fibrous material.
51. The absorbent core of claim 50 wherein said overall acquisition
zone is funnel-shaped.
52. The absorbent core of claim 50 wherein said overall acquisition
zone has a generally triangular shape.
53. An absorbent member having a back section and a front section
contiguous with said back section, said front section having an end
region and a deposition region contiguous with said end region and
said back section so that said deposition region is positioned
between said end region and said back section, the absorbent member
comprising:
a mixture of hydrophilic fibrous material and discrete particles of
absorbent gelling material;
a storage zone positioned in at least said deposition region of the
absorbent member; and
an acquisition zone positioned in said deposition region of the
absorbent member, said acquisition zone having a density of from
about 0.03 to about 0.15 g/cm.sup.3 ; said acquisition zone having
a lower average density and a lower average basis weight per unit
area than said storage zone, said acquisition zone extending from
the top surface of the absorbent member through the entire
thickness of the absorbent member, the top surface area of said
acquisition zone being completely positioned within said deposition
region and comprising less than about 35% of the top surface area
of said deposition region, said storage zone laterally surrounding
the perimeter of said acquisition zone so as to be in liquid
communication with the lateral area of said acquisition zone.
54. The absorbent member of claim 53 wherein the absorbent member
has a uniform thickness.
55. The absorbent member of claim 54 wherein the absorbent member
comprises a substantially uniform mixture of hydrophilic fibrous
material and discrete particles of absorbent gelling material
distributed throughout the absorbent member.
56. The absorbent member of claim 55 wherein said acquisition zone
has a rectangular cross-sectional area.
57. The absorbent member of claim 56 wherein the ratio of the
average density of said storage zone to the average density of said
acquisition zone is about equal to or greater than 1.25:1.
58. The absorbent member of claim 57 wherein said mixture of
hydrophilic fibrous material and said particles of absorbent
gelling material are disposed in the absorbent member in a
fiber-to-particulate weight ratio of from about 40:60 to about
98:2.
59. The absorbent member of claim 58 wherein said back section has
less average basis weight per unit area than said storage zone
positioned in said deposition region.
60. The absorbent member of claim 59 wherein the top surface area
of said acquisition zone has a generally triangular shape.
61. The absorbent member of claim 60 wherein the absorbent member
has an asymmetric shape.
62. The absorbent member of claim 61 wherein the top surface area
of said acquisition zone comprises less than about 20% of the top
surface area of said deposition region.
63. The absorbent member of claim 62 wherein the ratio of the
average density of said storage zone to the average density of said
acquisition zone is about equal to or greater than 1.5:1.
64. The absorbent member of claim 58 wherein the top surface area
of said acquisition zone has an hourglass shape.
65. The absorbent member of claim 58 wherein said acquisition zone
comprises plural acquisition zones.
66. An absorbent article comprising:
a liquid pervious topsheet;
a liquid impervious backsheet associated with said topsheet;
and
an absorbent member according to claims 53, 54, 55, 57, 58, 60, 61,
63, 64 or 65 positioned between said topsheet and said
backsheet.
67. An absorbent member having a back section and a front section
contiguous with said back section, said front section having an end
region and a deposition region contiguous with said end region and
said back section so that said deposition region is positioned
between said end region and said back section, the absorbent member
comprising:
a mixture of hydrophilic fibrous material and discrete particles of
absorbent gelling material;
a storage zone positioned in at least said deposition region of the
absorbent member; and
an acquisition zone positioned in said deposition region of the
absorbent member, said acquisition zone having a density of from
about 0.05 to about 0.41 g/cm.sup.3, said acquisition zone having a
lower average density and a lower average basis weight per unit
area than said storage zone, said acquisition zone extending from
the top surface of the absorbent member through a fraction of the
total thickness of the absorbent member, the top surface area of
said acquisition zone being completely positioned within said
deposition region and comprising less than about 35% of the top
surface area of said deposition region, said storage zone laterally
surrounding the perimeter of said acquisition zone so as to be in
liquid communication with the lateral area of said acquisition
zone.
68. The absorbent member of claim 67 wherein said storage zone and
said acquisition zone have the same thickness.
69. The absorbent member of claim 68 wherein the absorbent member
has a uniform thickness.
70. The absorbent member of claim 69 wherein said back section does
not comprise said storage zone.
71. The absorbent member of claim 70 wherein only said storage zone
comprises said mixture of hydrophilic fibrous material and discrete
particles of absorbent gelling material.
72. The absorbent member of claim 70 wherein only said storage zone
and said acquisition zone comprise said mixture of hydrophilic
fibrous material and discrete particles of absorbent gelling
material.
73. The absorbent member of claim 72 wherein the top surface area
of said acquisition zone has a generally triangular shape.
74. The absorbent member of claim 73 wherein the absorbent member
has an asymmetric shape.
75. An absorbent article comprising:
a liquid pervious topsheet;
a liquid impervious backsheet associated with said topsheet;
and
an absorbent member according to claims 67, 69, 72, 73 or 74
positioned between said topsheet and said backsheet.
76. A disposable diaper comprising:
a liquid pervious topsheet;
a liquid impervious backsheet associated with said topsheet;
an absorbent member according to claims 1, 48, 53 or 67 positioned
between said topsheet and said backsheet; and
an elastic member disposed along each longitudinal edge of said
disposable diaper.
77. An absorbent core comprising:
an absorbent member comprising a mixture of hydrophilic fibrous
material and discrete particles of absorbent gelling material;
and
an absorbent acquisition core positioned adjacent said absorbent
member, said absorbent acquisition core comprising a mixture of
hydrophilic fibrous material and up to about 8% by weight of said
absorbent acquisition core of discrete particles of absorbent
gelling material; a storage zone positioned in at least a portion
of said absorbent acquisition core; and a core acquisition zone
positioned in said absorbent acquisition core, said core
acquisition zone having a density and basis weight per unit area
greater than zero, said core acquisition zone having a lower
average density and a lower average basis weight per unit area than
said storage zone, said core acquisition zone extending from the
top surface of the absorbent member through the entire thickness of
the absorbent acquisition core, the top surface area of said core
acquisition zone comprising less than about 35% of the top surface
area of said absorbent acquisition core, said storage zone
laterally surrounding the perimeter of said core acquisition zone
so as to be in liquid communication with the lateral area of said
core acquisition zone.
78. An absorbent article having a front region, a back region, and
a crotch region disposed between said front region and said back
region, said absorbent article comprising:
a liquid pervious topsheet;
a liquid impervious backsheet associated with said topsheet;
an absorbent member comprising a mixture of hydrophilic fibrous
material and discrete particles of absorbent gelling material;
and
an absorbent acquisition core positioned between said topsheet and
said absorbent member, said absorbent acquisition core comprising a
mixture of hydrophilic fibrous material and up to about 8% by
weight of said absorbent acquisition core of discrete particles of
absorbent gelling material; a storage zone positioned in at least
said crotch region of said absorbent article; and a core
acquisition zone positioned in said crotch region of said absorbent
article, said core acquisition zone having a density and basis
weight per unit area greater than zero, said core acquisition zone
having a lower average density and a lower average basis weight per
unit area than said storage zone, said core acquisition zone
extending from the top surface of the absorbent member through the
entire thickness of the absorbent member, the top surface area of
said core acquisition zone comprising less than about 35% of the
top surface area of said absorbent member, said storage zone
laterally surrounding the perimeter of said core acquisition zone
so as to be in liquid communication with the lateral area of said
core acquisition zone.
Description
FIELD OF THE INVENTION
This invention relates to absorbent members having a mixture of
hydrophillic fibrous material and discrete particles of an
absorbent gelling material. More particularly, the invention
relates to a relatively high density absorbent member having a
relatively lower average density and lower average basis weight
acquistion zone positioned in the area of typical liquid deposition
to more quickly acquire and distribute liquids within the absorbent
member.
BACKGROUND OF THE INVENTION
Absorbent articles such as disposable diapers, adult incontinent
pads, sanitary napkins and the like are generally provided with
absorbent members to receive and retain body liquids. In order for
such absorbent articles to function efficiently, the absorbent
members must quickly acquire body liquids into the structure from
the point of application and subsequently distribute the body
liquids within and throughout the absorbent member to provide
maximum leakage containment. In addition, the absorbent members
should be capable of retaining liquids when placed under loads.
Prior art attempts to improve the effectiveness of such absorbent
members have included distributing particles of absorbent gelling
material throughout or in portions of the absorbent member. For
example, Procter & Gamble; European Patent Application
EP-A-122,042; published Oct. 17, 1984 discloses absorbent members
wherein particles of absorbent gelling material (hydrogel) are
dispersed in an air-laid web of hydrophilic fibrous material and
compressed to a particular density. In addition, United States
patent application Ser. No. 734,426; filed May 15, 1985, by Paul T.
Weisman, Dawn I. Houghton and Dale A. Gellert discloses a
dual-layer absorbent core wherein an absorbent acquisition layer
overlays a lower fluid storage layer that consists essentially of a
uniform combination of hydrophilic fibrous material and discrete
particles of absorbent gelling material.
Absorbent gelling materials are polymeric materials which are
capable of absorbing large quantities of liquids relative to their
weight such as water and body wastes, and which are further capable
of retaining such absorbed liquids under moderate pressures. These
absorption characteristics of absorbent gelling materials make them
especially useful for incorporation into absorbent articles such as
disposable diapers, adult incontinent pads, sanitary napkins and
the like. However, in spite of the extremely high absorption
capacities of such absorbent gelling materials, their performance
when used in disposable absorbent articles has still not been
optimized.
The effectiveness of absorbent gelling materials in disposable
absorbent articles is quite dependent upon the form, position,
and/or manner in which the particles of absorbent gelling material
are incorporated into the absorbent member. In some cases, for
example, the effectiveness of absorbent members containing
particles of absorbent gelling material can be adversely affected
by a phenomenon called gel blocking. The term gel blocking
describes a situation that occurs when a particle of absorbent
gelling material is wetted, the surface of the particles swelling
so as to inhibit liquid transmission into the interior of the
absorbent member. Wetting of the interior of the absorbent member,
therefore, takes place via a very slow diffusion process. In
practical terms, this means that acquisition of liquids by the
absorbent member is much slower than the discharge of the liquid to
be absorbed, and leakage from the absorbent article may take place
well before the particles of absorbent gelling material in the
absorbent member are fully saturated or before the liquid can
diffuse or wick past the "blocking" particles into the rest of the
absorbent member. The slow acquisition rate also fails to take
advantage of the rapid wicking of liquids to other parts of the
absorbent member provided by a densified absorbent member
containing particles of absorbent gelling material.
Thus, it would be advantageous to provide an absorbent member that
more quickly acquires and distributes liquids within itself while
minimizing gel blocking during the liquid acquisition phase. It is
therefore a primary objective of the present invention to provide
absorbent members which are especially effective and efficient in
their use of absorbent gelling materials.
SUMMARY OF THE INVENTION
The present invention provides an absorbent article such as
disposable diapers, incontinent pads, sanitary napkins or the like
that has an absorbent member that is suitable for acquiring and
containing liquids in an especially effective and efficient manner.
Such an absorbent article comprises a liquid pervious topsheet, a
liquid impervious backsheet, and an absorbent member positioned
between the topsheet and the backsheet.
The absorbent member has a deposition region which comprises a
storage zone of a relatively high density and high basis weight to
absorb and retain liquids acquired by the absorbent member and an
acquisition zone of a relatively lower average density and lower
average basis weight than the storage zone to quickly acquire and
temporarily hold discharged liquids. The absorbent member also
comprises a mixture of hydrophilic fibrous material and discrete
particles of absorbent gelling material.
In accordance with one aspect of the present invention, the
acquisition zone is positioned toward the front of the absorbent
member so that the acquisition zone may be positioned in the area
of typical liquid deposition. The acquisition zone is also sized so
that the top surface area of the acquisition zone comprises less
than about 50% of the top surface area of the front section of the
absorbent member.
In accordance with another aspect of the present invention, the
ratio of the average density of the storage zone to the average
density of the acquisition zone is preferably about equal to or
greater than 1.25:1, and most preferably about equal to or greater
than 2:1. The acquisition zone preferably has a density of from
about 0.05 to about 0.15 g/cm.sup.3 ; the acquisition zone also
preferably having a uniform density and uniform basis weight
throughout.
In a preferred embodiment of the present invention, a relatively
high gel strength absorbent gelling material is mixed with
hydrophilic fibrous material to not only minimize gel blocking but
also to help maintain an open capillary structure within the
absorbent member to enhance planar transport of liquids away from
the area of typical liquid deposition to the rest of the absorbent
member. The mixture of hydrophilic fibrous material and discrete
particles of absorbent gelling material preferably have a
fiber-to-particulate weight ratio of from about 40:60 to about
98:2, more preferably about 50:50 to about 91:9.
The present invention also relates to dual-layer absorbent cores of
the type having an absorbent acquisition core which consists
essentially of hydrophilic fibrous material and an absorbent member
which consists of a mixture of hydrophilic fibrous material and
discrete particles of absorbent gelling material. The absorbent
member has a top surface area which is from about 0.25 to about 1.0
times the top surface area of the absorbent acquisition core. The
absorbent member is further positioned relative to the backsheet of
the absorbent article in which its positioned such that at least
about 75% of the absorbent gelling material is found within the
front two-thirds portion of the absorbent article. The acquisition
zone of the absorbent member is also positioned relative to the
backsheet such that it is completely positioned within the front
two-thirds portion of the absorbent article.
DETAILED DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims which particularly
point out and distinctly claim the subject matter regarded as
forming the present invention, it is believed the invention will be
better understood from the following description taken in
conjunction with the accompanying drawings in which:
FIG. 1 is a plan view of a disposable diaper embodiment of the
present invention wherein most of the topsheet has been cut-away to
more clearly show the underlying absorbent member of the
diaper;
FIG. 2 is a longitudinal sectional view of only the absorbent
member of the disposable diaper taken along sectional line 2--2 of
FIG. 1;
FIG. 3 is a transverse sectional view of only the absorbent member
of the disposable diaper taken along sectional line 3--3 of FIG.
1;
FIG. 4 is a perspective view of the absorbent member of the
disposable diaper shown in FIG. 1;
FIG. 5 is a perspective view of an alternative embodiment of the
absorbent member of the present invention;
FIG. 6 is a perspective view of a dual-layer absorbent core having
a further alternative embodiment of the absorbent member of the
present invention;
FIG. 7 is a sectional view of the dual-layer absorbent core of FIG.
6 taken along sectional line 7--7 of FIG. 6; and
FIG. 8 is a plan view of a still further alternative embodiment of
the absorbent member of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The absorbent members of the present invention will be described
herein in relationship to their use in disposable absorbent
articles; however, it should be understood that the potential
application of the absorbent members of the present invention
should not be limited to disposable absorbent articles. As used
herein, the term "disposable absorbent article" refers to articles
which absorb and contain body exudates and more specifically refers
to articles which are placed against or in proximity to the body of
the wearer to absorb and contain the various exudates discharged
from the body, and which are intended to be discarded after a
single use (i.e., they are not intended to be laundered or
otherwise restored or reused). A preferred embodiment of a
disposable absorbent article, diaper 20, is shown in FIG. 1. As
used herein, the term "diaper" refers to a garment generally worn
by infants and incontinent persons that is worn about the lower
torso of the wearer. It should be understood, however, that the
present invention is also applicable to other disposable absorbent
articles such as incontinent briefs, sanitary napkins, and the
like.
FIG. 1 is a plan view of the diaper 20 of the present invention in
its flat-out, uncontracted state (i.e., with all elastic induced
contraction removed) with portions of the structure being cut-away
to more clearly show the construction of the diaper 20 and with the
portion of the diaper 20 which contacts the wearer facing the
viewer. The diaper 20 is shown in FIG. 1 to have a front waistband
region 22, a back waistband region 24, a crotch region 26 and a
periphery 28 which is defined by the outer edges of the diaper in
which the longitudinal edges are designated 30 and the end edges
are designated 32. The diaper additionally has a transverse
centerline which is designated 34 and a longitudinal centerline
which is designated 36.
The diaper 20 comprises a liquid pervious topsheet 38; a liquid
impervious backsheet 40; an absorbent member 42; and elastic
members 44. While the topsheet 38, the backsheet 40, the absorbent
member 42, and the elastic members 44 may be assembled in a variety
of well known configurations, a preferred diaper configuration is
described generally in U.S. Pat. No. 3,860,003 entitled
"Contractable Side Portions for Disposable Diaper", which issued to
K. B. Buell on Jan. 14, 1975, and which patent is incorporated
herein by reference.
FIG. 1 shows a preferred embodiment of the diaper 20 in which the
topsheet 38 and the backsheet 40 are co-extensive and have length
and width dimensions generally larger than those of the absorbent
member 42. The topsheet 38 is associated with and superimposed on
the backsheet 40 thereby forming the periphery 28 of the diaper 20.
The periphery 28 defines the outer perimeter or the edges of the
diaper 20. The periphery 28 comprises the end edges 32 and
longitudinal edges 30.
The diaper 20 has front and back waisband regions 22 and 24
respectively, extending from the end edges 32 of the diaper
periphery 28 toward the transverse centerline 34 of the diaper a
distance from about 2% to about 10%, preferably about 5%, of the
length of the diaper 20. The waistband regions comprise those upper
portions of the diaper 20, which when worn, encircle the waist of
the wearer. The crotch region 26 is that portion of the diaper 20
between the waistband regions 22 and 24, and comprises that portion
of the diaper 20 which, when worn, is positioned between the legs
of the wearer and covers the lower torso of the wearer. Thus, the
crotch region 26 defines the area of typical liquid deposition for
a diaper 20 or other disposable absorbent article.
The topsheet 38 is compliant, soft feeling, and non-irritating to
the wearer's skin. Further, the topsheet 38 is liquid pervious
permitting liquids to readily penetrate through its thickness. A
suitable topsheet 38 may be manufactured from a wide range of
materials, such as porous foams, reticulated foams, apertured
plastic films, natural fibers (e.g., wood or cotton fibers),
synthetic fibers (e.g., polyester or polypropylene fibers) or from
a combination of natural and synthetic fibers. Preferably, the
topsheet 38 is made of a hydrophobic material to isolate the
wearer's skin from liquids in the absorbent member 42.
A particularly preferred topsheet 38 comprises staple length
polypropylene fibers having a denier of about 1.5, such as Hercules
type 151 polypropylene marketed by Hercules, Inc. of Wilmington,
Del. As used herein, the term "staple length fibers" refers to
those fibers having a length of at least about 15.9 mm (0.62
inches).
There are a number of manufacturing techniques which may be used to
manufacture the topsheet 38. For example, the topsheet 38 may be
woven, non-woven, spunbonded, carded, or the like. A preferred
topsheet is carded, and thermally bonded by means well known to
those skilled in the fabrics art. Preferably, the topsheet 38 has a
weight from about 18 to about 25 grams per square meter, a minimum
dry tensile strength of at least about 400 grams per centimeter in
the machine direction and a wet tensile strength of at least about
55 grams per centimeter in the cross machine direction.
The backsheet 40 is impervious to liquids and is preferably
manufactured from a thin plastic film, although other flexible
liquid impervious materials may also be used. The backsheet 40
prevents the exudates absorbed and contained in the absorbent
member 42 from wetting articles which contact the diaper 20 such as
bed sheets and undergarments. Preferably, the backsheet 40 is
polyethylene film having a thickness of from about 0.012 mm (0.5
mil) to about 0.051 centimeters (2.0 mils), although other
flexible, liquid impervious materials may be used. As used herein,
the term "flexible" refers to materials which are compliant and
which will readily conform to the general shape and contours of the
wearer's body.
A suitable polyethylene film is manufactured by Monsanto Chemical
Corporation and marketed in the trade as Film No. 8020. The
backsheet 40 is preferably embossed and/or matte finished to
provide a more clothlike appearance. Further, the backsheet 40 may
permit vapors to escape from the absorbent member 42 while still
preventing exudates from passing through the backsheet 40.
The size of the backsheet 40 is dictated by the size of the
absorbent member 42 and the exact diaper design selected. In a
preferred embodiment, the backsheet 40 has a modified
hourglass-shape extending beyond the absorbent member 42 a minimum
distance of at least about 1.3 centimeters to about 2.5 centimeters
(about 0.5 to about 1.0 inch) around the entire diaper periphery
28.
The topsheet 38 and the backsheet 40 are associated together in any
suitable manner. As used herein, the term "associated" encompasses
configurations whereby the topsheet 38 is directly joined to the
backsheet 40 by affixing the topsheet 38 directly to the backsheet
40, and configurations whereby the topsheet 38 is indirectly joined
to the backsheet 40 by affixing the topsheet 38 to intermediate
members which in turn are affixed to the backsheet 40. In a
preferred embodiment, the topsheet 38 and the backsheet 40 are
affixed directly to each other in the diaper periphery 28 by
attachment means (not shown) such as an adhesive or any other
attachment means as known in the art. For example, a uniform
continuous layer of adhesive, a patterned layer of adhesive, or an
array of separate lines or spots of adhesive may be used to affix
the topsheet 38 to the backsheet 40.
Tape tab fasteners 46 are typically applied to the back waistband
region 24 of the diaper 20 to provide a fastening means for holding
the diaper on the wearer. Only one of the tape tab fasteners is
shown in FIG. 1. The tape tab fasteners 46 can be any of those well
known in the art, such as the fastening tape disclosed in U.S. Pat.
No. 3,848,594 issued to K. B. Buell on Nov. 19, 1974, which patent
is incorporated herein by reference. These tape tab fasteners 46 or
other diaper fastening means, such as pins, are typically applied
near the corners of the diaper 20.
The elastic members 44 are disposed adjacent the periphery 28 of
the diaper 20, preferably along each longitudinal edge 30 so that
the elastic members 44 tend to draw and hold the diaper 20 against
the legs of the wearer. Alternatively, the elastic members 44 may
be disposed adjacent either or both of the end edges 32 of the
diaper 20 to provide a waistband as well as or rather than leg
cuffs. For example, a suitable waistband is disclosed in U.S. Pat.
No. 4,515,595 issued to David J. Kievit and Thomas F. Osterhage on
May 7, 1985, which patent is herein incorporated by reference. In
addition, a method and apparatus suitable for manufacturing a
disposable diaper having elastically contractible elastic members
is described in U.S. Pat. No. 4,081,301 entitled "Method and
Apparatus for Continuously Attaching Discrete, Stretched Elastic
Strands to Predetermined Isolated Portions of Disposable Absorbent
Products" which issued to K. B. Buell on Mar. 28, 1978 and which
patent is incorporated herein by reference.
The elastic members 44 are secured to the diaper 20 in an
elastically contractible condition so that in a normally
unrestrained configuration, the elastic members 44 effectively
contract or gather the diaper 20. The elastic members 44 can be
secured in an elastically contractible condition in at least two
ways. For example, the elastic members 44 may be stretched and
secured while the diaper 20 is in an uncontracted condition.
Alternatively, the diaper 20 may be contracted, for example, by
pleating, and the elastic members 44 secured and connected to the
diaper 20 while the elastic members 44 are in their unrelaxed or
unstretched condition.
In the embodiment illustrated in FIG. 1, the elastic members 44
extend essentially the entire length of the diaper 20 in the crotch
region 26. Alternatively the elastic members 44 may extend the
entire length of the diaper 20, or any other length suitable to
provide an elastically contractable line. The length of the elastic
members 44 is dictated by the diapers' design.
The elastic members 44 may take a multitude of configurations. For
example, the width of the elastic members 44 may be varied from
about 0.25 millimeters (0.01 inches) to about 25 millimeters (1.0
inch) or more; the elastic members 44 may comprise a single strand
of elastic material or may comprise several parallel or
non-parallel strands of elastic material; or the elastic members 44
may be rectangular or curvilinear. Still further, the elastic
members 44 may be affixed to the diaper in any of several ways
which are known in the art. For example, the elastic members 44 may
be ultrasonically bonded, heat and pressure sealed into the diaper
20 using a variety of bonding patterns or the elastic members 44
may simply be glued to the diaper 20.
The absorbent member 42 is positioned between the topsheet 38 and
the backsheet 40 to form the diaper 20. The absorbent member 42 is
generally compressible, conformable, non-irritating to the wearer's
skin, and capable of absorbing and retaining liquids and certain
body exudates. It should be understood that for purposes of this
invention that an absorbent member is not necessarily limited to a
single layer or sheet of material. Thus, the absorbent member 42
may actually comprise laminates or combinations of several sheets
or webs of the requisite types of materials as hereinafter
described. Thus as used herein, the term "member" includes the term
"members" or "layers" or "layered."
FIG. 4 is a perspective view of a preferred embodiment of the
absorbent member 42 of the present invention. The absorbent member
42 is shown in FIG. 4 to comprise a back section 48 and a front
section 50. The front section 50 is shown to have an end region 52
and a deposition region 54. The deposition region 54 comprises an
acquisition zone 56 (shown by the dotted lines) and a storage zone
58. Further, the front section 50 is transversely divided into
three regions comprising two transversely spaced ear regions 60 and
62 respectively, and a central region 64. The absorbent member 42
additionally has a transverse centerline which is designated 66 and
a longitudinal centerline which is designated 68.
The absorbent member 42 has a back section 48 and a front section
50 that is contiguous with the back section 48. The back section 48
and the front section 50 of the absorbent member 42 extend
respectively from the end edges 70 of the absorbent member 42
toward the transverse centerline 66, the front portion 50 extending
a distance from about one half to about three-fourths, preferably
about two-thirds, of the length of the absorbent member 42. The
front section 50 is preferably greater than one half of the total
length of the absorbent member 42 so that it will encompass all of
the area of typical liquid deposition of an absorbent member 42
when it is placed in a diaper or other absorbent article.
The front portion 50 has an end region 52 and a deposition region
54. The end region 52 comprises that portion of the front section
50 extending from the respective end edge 70 of the absorbent
member 42 toward the transverse centerline 66 a distance from about
2% to about 10%, preferably about 5%, of the length of the
absorbent member 42. The deposition region 54 comprises that
portion of the front portion 50 that is contiguous with and
positioned between the end region 52 and the back section 48 and
encompasses the area of typical liquid deposition of the absorbent
member 42.
The front portion 50 further has two transversely spaced ear
regions 60 and 62 respectively, and a central region 64 disposed
intermediate said ear regions 60 and 62. The ear regions 60 and 62
comprise those portions which generally extend from the
longitudinal edges 30 of the periphery 28 toward the longitudinal
centerline a distance from about one-tenth to about one-third of
the width of the absorbent member 42. Thus, the ear regions 60 and
62 are those portions that engage the side marginal portions of the
wearer's waist and torso, whereas the central region 64 engages the
medial portion of the wearer's waist and torso. The central region
thus defines the transverse area of typical liquid deposition.
The absorbent member 42 may be manufactured in a wide variety of
sizes and shapes (e.g., rectangular, hourglass, asymmetrical, etc.)
and from a wide variety of materials. The total absorbent capacity
of the absorbent member 42 should, however, be compatible with the
design liquid loading for the intended use of the absorbent article
or diaper. Further, the size and absorbent capacity of the
absorbent member 42 may be varied to accommodate wearers ranging
from infants through adults. The absorbent member 42 preferably
comprises a mixture of hydrophilic fibrous material and particular
amounts of discrete particles of absorbent gelling material.
Various types of hydrophilic fibrous material can be used in the
absorbent member 42. Any type of hydrophilic fibrous material which
is suitable for use in conventional absorbent products are suitable
for use in the absorbent member 42 of the present invention.
Specific examples of such hydrophilic fibrous material include
cellulose fibers, rayon, and polyester fibers. Other examples of
suitable hydrophilic fibrous materials include hydrophilized
hydrophobic fibers, such as surfactant-treated or silica-treated
thermoplastic fibers. For reasons of availability and cost,
cellulose fibers, in particular wood pulp fibers which are also
referred to as airfelt, are preferred.
As used herein, the term "hydrophilic" describes fibers or the
surfaces of fibers which are wetted by the liquids deposited onto
the fibers. The state of the art respecting wetting of materials
allows definition of hydrophilicity (and wetting) in terms of
contact angles and the surface tension of the liquids and solids
Invovled. This is discussed in detail in The American Chemical
Society publication entitled Contact Angle, Wetability, and
Adhesion edited by Robert F. Gould and copyrighted in 1964. A fiber
or surface of a fiber is said to be wetted by a liquid either when
the contact angle between the liquid and the fiber or surface is
less than 90.degree. or when the liquid will tend to spread
spontaneously across the surface; both conditions normally
coexist.
In addition to hydrophilic fibrous material, the absorbent member
42 also contains particular amounts of discrete particles of
absorbent gelling material. Such absorbent gelling material may be
inorganic or organic compounds capable of absorbing liquids and
retaining them under moderate pressures.
Suitable absorbent gelling materials can be inorganic materials
such as silica gels or organic compounds such as cross-linked
polymers. Cross-linking may be by covalent, ionic, van der Waals,
or hydrogen bonding. Examples of absorbent gelling material
polymers include polyacrylamides, polyvinyl alcohol, ethylene
maleic anhydride copolymers, polyvinyl ethers, hydroxypropyl
cellulose, carboxymethyl cellulose, polyvinylmorpholinone, polymers
and copolymers of vinyl sulfonic acid, polyacrylates,
polyacrylamides, polyvinyl pyridine and the like. Other suitable
hydrogels are disclosed in Assarson et al., U.S. Pat. No. 3,901,236
issued Aug. 26, 1975, which patent is incorporated herein by
reference. Particularly preferred polymers for use in the absorbent
member are hydrolized, acrylonitrile grafted starch, acrylic acid
grafted starch, polyacrylates and isobutylene maleic anhydride
copolymers, or mixtures thereof.
Processes for preparing hydrogels are disclosed in Masuda et al.,
U.S. Pat. No. 4,076,663, issued Feb. 28, 1978; Tsubakimoto et al.
U.S. Pat. No. 4,286,082, issued Aug. 25, 1981; and further in U.S.
Pat. Nos. 3,734,876, 3,661,815, 3,670,731, 3,664,343, 3,783,871 and
Belgium Pat. No. 785,850, which patents are all incorporated herein
by reference.
Absorbent gelling material used in the absorbent member 42 is in
the form of discrete "particles". Particles of absorbent gelling
material can be of any desired shape, e.g., spiral or semi-spiral,
cubic, rod-like, polyhedral, etc. Shapes having a large greatest
dimension/smallest dimension ratio, like needles, flakes, and
fibers, are also contemplated for use herein. Conglomerates of
particles of absorbent gelling material may also be used in the
absorbent member 42.
Although the absorbent gelling material-containing absorbent member
is expected to perform well with particles having a size varying
over a wide range, other considerations may preclude the use of
very small or very large particles. For reasons of industrial
hygiene, average particle sizes smaller than about 30 microns are
less desirable. Particles having a smallest dimension larger than
about 2 millimeters may also cause a feeling of grittiness in the
absorbent member, which is undesirable from a consumer aesthetics
standpoint. Furthermore, the rate of fluid absorption is affected
by particle size. Larger particles have very much reduced rates of
absorption. Preferred for use herein are particles having an
average size of from about 50 microns to about 1 millimeter.
"Particle size" as used herein means the weighted average of the
smallest dimension of the individual particles.
Although most absorbent gelling materials will perform well in the
absorbent member 42 of the present invention, absorbent gelling
materials having high gel strength are particularly useful. Gel
strength must be such that the particles of absorbent gelling
material do not deform and fill to an unacceptable degree the
capillary void space in the absorbent member 42, thereby inhibiting
both absorbent capacity of the structure and fluid distribution
throughout the structure.
Gel strength refers to the tendency of the particles of absorbent
gelling material to deform or spread under stress once the
particles absorb liquids. For a given type of absorbent gelling
material, gel strength will generally decrease as the gel volume
increases. It has been found that it is desirable to utilize an
absorbent member 42 whose polymer materials have as high a gel
strength as possible consistent with the realization of absorbent
gelling materials of acceptably high gel volume.
It has been found that gel strength, i.e. gel deformation tendency,
(in the context of absorbent gelling materials incorporated into
absorbent members and absorbent articles) correlates directly with
the shear modulus of the absorbent gelling material. Accordingly,
polymer materials of absorbent gelling material having sufficient
gel strength can be appropriately characterized by specifying gel
strength in terms of the shear modulus of the particles of
absorbent gelling material.
Shear modulus can be conventionally measured, for example, by a
procedure which involves the use of a stress rheometer to determine
the ratio of (a) stress applied to a given sample versus (b) the
resulting strain exhibited by the sample. The absorbent gelling
material sample tested in this manner is swollen to its gel volume
with synthetic urine. Using a procedure described in greater detail
hereinafter, the stress/strain ratio is determined. The shear
modulus of the resulting sample in dynes/cm.sup.2 is then
subsequently calculated from this ratio. Absorbent gelling
materials which have been found to be particularly useful in the
present invention exhibit a shear modulus of at least about 2,000
dynes/cm.sup.2. More preferably, the absorbent gelling materials
have a shear modulus within the range of about 2500 to about 92,000
dynes/cm.sup.2 and most preferably of from about 5,000 to about
35,000 dynes/cm.sup.2.
Without wishing to be bound by any particular theory, it is
believed that absorbent gelling materials having high gel strength
as reflected in their shear modulus values will resist deformation
upon fluid absorption and will have a reduced tendency to flow into
the void spaces between fibers. Thus, high gel strength absorbent
gelling materials may actually serve to maintain separation of the
individual fibers of the hydrophilic fibrous material. Such fiber
separation improves both the wicking and the absorbent capacity of
such absorbent members. Low gel strength materials, on the other
hand, merely flow into the void spaces between the fibers upon
fluid absorption and can thereby actually reduce the acquisition
rate and the absorbent capacity of the absorbent members and
absorbent articles into which they are incorporated.
Gel strength of absorbent gelling materials is quantified by means
of determining the shear modulus of a sample of the swollen
particles. Shear modulus is determined using a stress rheometer
which comprises a circular lower plate onto which the swollen
particle sample is placed. A truncated conical upper element having
the same projected surface area as the area of the lower circular
plate is positioned above the circular lower plate. This upper
element is lowered into the mass of swollen particle material on
the circular lower plate and is positioned at the proper gap
relative to the circular lower plate. This gap corresponds to the
point at which an untruncated cone would contact the lower
plate.
An oscillating torque (stress) is applied torsionally to the
conical element, and the resulting angular displacement of the cone
is determined as a function of the applied torque.
The sample being tested is swollen to its gel volume in synthetic
urine. Synthetic Urine is typically 15.0 parts of 1% Triton X-100,
60.0 parts of NaCl, 1.8 parts of CaCl.sub.2. 2H.sub.2 O, and 3.6
parts of MgCL.sub.2. 6H.sub.2 O, diluted to 6000 parts with
distilled H.sub.2 O. The resulting solution has an absorbance of
about 0.25 at its absorbence maximum of 617 mm.
Excess free synthetic urine is removed from the sample by blotting,
and approximately 1.5 cc of the swollen material is placed in the
gap between the lower circular plate and the upper conical element
of the rheometer. This mass is usually formed from an agglomeration
of swollen particles which have unswollen particle dimensions less
than 710 microns. Spherical particles should be ground to form
irregular shaped particles before testing.
Stress and strain measurements are taken under the following
conditions:
______________________________________ Parameter Value
______________________________________ Type of Rheometer Sangamo
Visco-elastic Analyzer Configuration Oscillating Cone and Plate
Plate Radius 2.5 cm Cone Radius 2.5 cm (Edge to vertex) Cone Angle*
43.6 milliradians Oscillation Frequency 1.0 Hertz Strain Amplitude
2.5% Sample Temperature 21.4.degree. C.
______________________________________ *Angle between surface of
the lower plate and the surface of the cone i.e (Pi/2 semivertical
angle).
Under these conditions, an oscillatory torque (stress) is applied
via the upper conical element to the swollen particles. This
results in an oscillatory response (strain) of the sample which is
reflected by the magnitude of the angle through which the conical
element rotates in response to the applied torque. The shear
modulus of the particles is calculated from the ratio of (i) the
applied stress to (ii) the amplitude of the in-phase component of
the resultant strain.
For the particular cone/plate geometry employed in this testing,
the ratio of stress (g-cm) to strain (milliradians) is converted to
shear modulus (dynes/cm.sup.2) using the following formula:
##EQU1## wherein the cone angle and strain are expressed in units
of milliradians, the plate radius in units of cm and torque in
units of g-cm. For absorbent gelling materials, the phase angle is
close to zero and so the cosine of the phase angle is taken as
unity. The factor 981 is that which converts g-cm to dyne-cm. Thus
##EQU2## for the particular equipment used in this test method.
The relative amount of hydrophilic fibrous material and particles
of absorbent gelling material used in the absorbent member 42 of
the present invention can be most conveniently expressed in terms
of a weight percentage of the absorbent member 42. The absorbent
member 42 preferably contains from about 2% to about 60%, more
preferably from about 10% to about 25% by weight, of the absorbent
member 42 of absorbent gelling material. This concentration of
absorbent gelling material can also be expressed in terms of a
weight ratio of fiber to particulate. These ratios may range from
about 40:60 to about 98:2. For most commercially available
absorbent gelling materials, the optimum fiber-to-particulate
weight ratio is in the range of from about 50:50 to about 91:9.
Based on a cost/performance analysis, ratios of from about 75:25 to
about 90:10 are most preferred for use in the absorbent member
42.
In addition, the particles of absorbent gelling material may be
dispersed in various weight ratios throughout different regions and
thicknesses of the absorbent member 42.
For example, the mixture of hydrophilic fibrous material and
particles of absorbent gelling material may be disposed only in the
deposition region 54 of the absorbent member 42 and not in the back
section 48 or the end region 52. In addition, the acquisition zone
56 need not comprise the fiber/particulate mixture. While an
acquisition zone 56 containing only hydrophilic fibrous material
may work satisfactorily in rapidly acquiring liquids, such an
embodiment is not preferred. When particles of an absorbent gelling
material are maintained in the acquisition zone 56, especially high
gel strength absorbent gelling materials, the particles help
maintain an open capillary structure when the acquisition zone 56
is wetted so as to enhance planar transport of liquids away from
the acquisition zone 56 to the rest of the absorbent member 42.
Thus, the acquisition zone 56 preferably contains a uniformly
distributed mixture of hydrophilic fibrous material and discrete
particles of absorbent gelling material. It is most preferred that
the particles are substantially uniformly dispersed throughout the
entire absorbent member 42.
The deposition region 54 comprises an acquisition zone 56 and a
storage zone 58 in liquid communication with at least a portion of
the acquisition zone 56. The acquisition zone 56 comprises portions
of the deposition region 54 designated by the dotted lines in FIG.
4. The storage zone 58 generally comprises the remainder of the
deposition region 54 and more preferably the remainder of the
absorbent member 42.
It has been found that a relative capillarity difference between
the acquisition zone 56 and the storage zone 58 is of importance in
the overall efficiency and effectiveness of the absorbent member
42. While liquid capillarity can be defined in several ways (e.g.,
pore size, density, basis weight, etc.), the density and basis
weight of the structure are the preferred parameters to define
liquid capillarity in the absorbent member 42 of the present
invention. Thus, the acquisition zone 56 must have both a
relatively lower average density and lower average basis weight per
unit area than the storage zone 48 to establish the preferred
capillary force gradient between them. Thus, the ratio of the
average density of the storage zone 58 to the average density of
the acquisition zone 56 should preferably be about equal to or
greater than about 1.25:1, more preferably about 1.5:1 and most
preferably about 2:1.
Without wishing to be bound by theory, it is believed that the
differential lower capillarity, the lower average density and lower
average basis weight, of the acquisition zone 56 in comparison to
the storage zone 58 is significant in achieving both a more
optimized liquid acquisition rate into the absorbent member 42 and
a relatively high liquid planar wicking rate throughout the
absorbent member 42. When an absorbent member 42 having a mixture
of hydrophilic fibrous material and particles of absorbent gelling
material is densified to the densities approximating those of the
storage zone 58, the liquid planar wicking rate becomes much
faster. It is believed that densifying the absorbent member 42
results in better planar wicking of liquid throughout the absorbent
member 42 (the x-y direction) because of the higher capillary force
due to the smaller pore size of the densified fibers. Densifying
the absorbent member 42 further results in a reduction in the bulk
of the structure (which is desirable from a consumer standpoint for
aesthetic reasons).
However, the densification of the absorbent member 42 also results
in a reduction in the rate of liquid acquisition into the absorbent
member 42 in the direction normal to planar wicking (i.e. the
z-direction). It is believed that as higher concentrations of
absorbent gelling material are located in the area of typical
liquid deposition, a maximum gel blocking effect is achieved,
thereby reducing the liquid acquisition rate. Thus, it is important
to provide a means for delivering the liquid into the absorbent
member 42 at a high rate. The acquisition zone 56 of lower average
density and lower average basis weight per unit area than the
densified absorbent member 42 or storage zone 58 provides such a
means. The acquisition zone 56 has a smaller concentration of
particles of absorbent gelling material in the area of typical
liquid deposition, thereby reducing the incidence of gel blocking
in this area during the liquid acquisition phase and thus improving
the liquid acquisition rate.
The capillary force gradient created at the interface between the
acquisition zone 56 and the storage area 58 also improves the
containment characteristics of the absorbent member 42. Liquids
deposited on the acquisition zone 56 tend to be acquired quickly
into the structure by the action of the acquisition zone 56.
Because the storage zone 58 has a higher capillarity than the
acquisition zone 56, the acquired liquids tend to be drawn into the
storage zone 58 and are then delivered to the other portions of the
storage zone 58 by the enhanced planar wicking rate achieved in the
storage zone 58; the liquids being retained even under moderate
pressure by the particles of absorbent gelling material in the
storage zone 58. Thus, it has been found that an absorbent member
42 having an acquisition zone 56 having a lower average density and
lower average basis weight per unit area than the storage zone 58
improves leakage containment by more quickly acquiring and
distributing liquids into and throughout the absorbent member
42.
In addition, it is believed that the acquisition zone 56 provides
an additional mechanism whereby an absorbent member 42 that has
already been wetted may contain and more readily acquire further
discharged liquids. A property of the particles of absorbent
gelling material is that they expand when wetted. Thus when the
absorbent member 42 is wetted, the particles of absorbent gelling
material in both the acquisition zone 56 and the storage zone 58
expand. However, because there is a greater concentration of
particles of absorbent gelling material in the higher average
density and higher average basis weight storage zone 58, the
storage zone 58 tends to expand to a greater thickness than the
acquisition zone 56. Thus, if the acquisition zone 56 is laterally
surrounded by the storage zone 58, a well or hole effect is
created. This "well" is advantageous for second depositions of
liquids because the liquids will tend to be drawn into the well
because it is in effect a zero density acquisition area. This is
especially helpful in the case of diapers for overnight use wherein
the wearer sleeps on the stomach because gravity additionally tends
to pull the later discharged liquids into the well whereupon they
distribute into the acquisition zone 56 and are wicked into the
storage zone 58. Thus, the acquisition zone 56 provides an
additional advantage for wetted absorbent members.
The storage zone 58 is thus the relatively high capillarity (high
density and high basis weight) portion of at least the deposition
region 54. The primary functions of the storage zone 58 are to
absorb discharged liquids that are either deposited directly onto
the storage zone 58 or transferred to the storage zone 58 via the
capillary force gradients established between the acquisition zone
56 and the storage zone 58, and to retain such liquids under the
pressures encountered as a result of the wearer's movements.
Preferably, the storage zone 58 consists essentially of the
structure disclosed in European Patent Application EP-A-122,042 or
the lower fluid storage layer disclosed in United States patent
application Ser. No. 734,426, both of which are incorporated herein
by reference, although other high capillarity structures may also
be used.
The storage zone 58 preferably has a relatively high density and a
high basis weight in relation to the acquisition zone 56. The
density and basis weight values of the storage zone 58 include the
weight of the particles of absorbent gelling material, such that
the density and basis weight values will vary depending upon the
amount of particles dispersed throughout the absorbent member 42.
Thus, the storage zone 58 will generally have a density of from
about 0.06 to about 0.4 g/cm.sup.3, and more preferably within the
range of from about 0.09 to about 0.20 g/cm.sup.3 for an absorbent
member 42 containing about 15% by weight of particles of absorbent
gelling material. The basis weight of such a storage zone 58 can
range from about 0.02 to about 0.186 g/cm.sup.2, preferably from
about 0.038 to about 0.12 g/cm.sup.2. For an absorbent member 42
containing about 50% by weight of particles of absorbent gelling
material, the density will typically range from about 0.1 to about
0.68 g/cm.sup.3 with a basis weight from about 0.034 to about 0.31
g/cm.sup.2. The density of the storage zone 58 is calculated from
its basis weight and caliper measured on newly unpacked, unfolded
and dissected diapers. The caliper is measured using a standard
guage with the sample under a "gentle" load of 10 g/cm.sup.2. The
basis weight is measured by die-cutting a certain size sample and
weighing the sample on a standard scale, the weight and area of the
sample determining the basis weight. (It should be noted that the
density and basis weight values include the weight of the particles
of absorbent gelling material.)
While the storage zone 58 may take on a number of sizes and shapes,
it is preferred that the storage zone 58 comprises the portion of
at least the deposition region 54 wherein there is no acquisition
zone 56. (i.e. The entire deposition region 54 comprises a storage
zone 58 except for the acquisition zone 56.) While the back section
48 and the end region 52 need not comprise storage zones, in the
particularly preferred embodiments of the absorbent member 42 as
shown in FIGS. 2, 3 and 4, the entire absorbent member 42 except
for the acquisition zone 56 consists of one or more storage zones
58. In addition, while the storage zone 58 need not completely
laterally surround the acquisition zone 56 (i.e. it is in liquid
communication with at least a portion of the lateral area of the
acquisition zone 56), in preferred embodiments of the present
invention, the storage zone 58 laterally surrounds the acquisition
zone 56 so as to take full advantage of the capillarity difference
between them.
The acquisition zone 56 has a relatively lower capillarity and thus
preferably a lower average density and a lower average basis weight
per unit area than the storage zone 58. The acquisition zone 56
serves to quickly collect and temporarily hold discharged liquids.
Since such liquids are generally discharged in gushes, the
acquisition zone 56 must be able to quickly acquire and transport
liquid by wicking from the point of liquid contact to other parts
of the absorbent member 42. The acquisition zone 56 preferably has
a density of from about 0.03 to about 0.24 g/cm.sup.3, more
preferably from about 0.05 to about 0.15 g/cm.sup.3 for an
absorbent member 42 containing about 15% by weight of particles of
absorbent gelling material. The basis weight of such an acquisition
zone 56 will preferably range from about 0.015 to about 0.1
g/cm.sup.2 and more preferably from about 0.018 to about 0.06
g/cm.sup.2. For an absorbent member 42 containing about 50% by
weight of particles of absorbent gelling material, the density will
typically range from about 0.05 to about 0.41 g/cm.sup.3 with a
basis weight of from about 0.025 to about 0.17 g/cm.sup.2. The
density of the acquisition zone 56 is calculated from its basis
weight and caliper measured on newly unpacked, unfolded and
dissected diapers. The caliper is measured using a standard guage
with the sample under a "gentle" load of 10 g/cm.sup.2. The basis
weight is measured by die-cutting a certain size sample and
weighing the sample on a standard scale, the weight and area of the
sample determining the basis weight. (The density and basis weight
values include the weight of the particles of absorbent gelling
material.)
While the acquisition zone 56 may conceivably have density and
basis weight values equal to zero, i.e. a hole or void space, such
an embodiment is not as preferred as an acquisition zone 56 having
some minimal value of density and basis weight. The transfer of
liquids through the topsheet 38 has been found to be diminished in
an absorbent member 42 having an acquisition zone 56 of zero
density and basis weight due to the lack of intimate contact
between any fibers of the acquisition zone 56 and the topsheet 38.
Thus, liquid may tend to pool or collect on the topsheet 38 thereby
creating a wet feeling for the wearer. Thus, it is preferred that
the acquisition zone 56 have some minimum density and basis
weight.
While the density and basis weight of the acquisition zone 56 may
vary throughout its area and thickness, such an embodiment is also
not preferred. The acquisition zone 56 preferably has a
substantially uniform density and uniform basis weight throughout
its area and thickness. This uniform density and basis weight
provides a uniform capillary force gradient across the interface
between the acquisition zone 56 and the storage zone 58 that
provides even liquid transfer.
The shape, size and positioning of the acquisition zone 56 is of
importance in determining the effectiveness of the resulting
absorbent member 42 in rapidly acquiring discharged liquids. In
accordance with the present invention, the acquisition zone 56
should be placed in a specific positional relationship with respect
to the area of typical liquid deposition of the absorbent member
42. While portions of the acquisition zone 56 may be positioned in
the back section 48 of the absorbent member 42, the acquisition
zone 56 is preferably positioned generally in the front section 50
of the absorbent member 42 so that the acquisition zone 56 is
positioned in the area of typical liquid deposition, i.e. the
deposition region 54. Thus, the acquisition zone 56 is placed in
the vicinity of the point of discharge of liquids so as to be
capable of quickly acquiring such liquids at their contact
zone.
The generally forward positioning of the acquisition zone 56 can be
defined by specifying the percentage of the top surface area of the
acquisition zone 56 which is found forward of particular points
along the length of the absorbent member 42. While the positioning
of the acquisition zone 56 can alternatively be defined with
respect to the volume of the acquisition zone positioned forward of
particular points, it has been found that the top surface area of
the acquisition zone 56 is a more desirable definition because the
top surface area actually defines the initial area available for
liquid acquisition. In addition, since the thickness of the
absorbent member 42 is preferably uniform in the deposition region
54 and the acquisition zone 56 has a generally rectangular
cross-sectional area, the top surface area definition is equal to a
volumetric definition in a preferred embodiment. Thus, the
positioning of the acquisition zone 56 will be referenced
throughout the specification as related to its top surface area.
(i.e. The percentage of the top surface area of the acquisition
zone positioned in a given area.)
Thus, in accordance with the present invention, at least a portion
of the acquisition zone 56 must be placed in the deposition region
54, even though the remaining portion may be positioned anywhere in
the absorbent member 42 including the back section 48 and the end
regions 52. (It being understood that if plural acquisition zones
are utilized, at least a portion of one of the acquisition zones
must be positioned in the deposition region 54.) However, the
acquisition zone 56 is preferably positioned relative to the
absorbent member 42 such that the top surface area of the
acquisition zone 56 is completely positioned within the front
section 50 of the absorbent member 42. More preferably, the
acquisition zone 56 is positioned relative to the absorbent member
42 such that the top surface area of the acquisition zone 56 is
completely positioned within the deposition region 54 of the
absorbent member 42. Even more preferably, at least 30% of the top
surface area of the acquisition zone 56 is positioned in the front
half of the front section (approximately the front 1/3 of the
overall absorbent member 42) of the absorbent member 42.
The forward positioning of the acquisition zone 56 may
alternatively be defined by specifying the percentage of the top
surface area of the acquisition zone 56 that is found forward of
particular points along the length of the diaper 20 or other
absorbent article. Thus, the acquisition zone 56 is preferably
positioned on the absorbent member 42 relative to the backsheet 40
such that at least a portion of the top surface area of the
acquisition zone 56 is in the crotch region 26 of the diaper 20.
More preferably, the acquisition zone 56 is positioned such that
its top surface area is completely positioned in the front
two-thirds portion of the diaper 20, most preferably in the front
half portion of the diaper 20; the top surface area also most
preferably being completely positioned in the crotch region 26 of
the diaper 20. (As noted herein, "portions" of the diaper 20 or
other absorbent article can be defined by reference to the top
surface area of the unfolded diaper 20 or absorbent article found
in front of a given point on the line which defines the length of
the diaper 20).
For purposes of determining the positioning of such acquisition
zone 56, the length of the absorbent member 42 or diaper 20 will be
taken as the normal longest longitudinal dimension of the elongated
structure. This normal longest dimension can be defined with
respect to the structure as it is applied to the wearer. When worn,
the opposing ends of the backsheet are fastened together so that
the ends form a circle around the wearer's waist. The normal length
of the absorbent member 42 or diaper 20 will thus be the length of
the line running through the absorbent member 42 or diaper 20 from
the point on the edge of it at the middle of the wearer's back
waist, through the crotch, to the point on the opposite edge of the
absorbent member 42 or diaper 20 at the middle of the wearer's
front waist.
The top surface area of the acquisition zone 56 may be found using
either of two techniques. The primary and simplest way is to place
the absorbent member 42 on a standard light box, such as the
transluminator model manufactured by Aristo grid Lamp Products,
Inc. The acquisition zone 56, because it has a lower average
density and lower average basis weight than the surrounding storage
zone 58, will appear lighter or brighter due to the fact that more
light will be transmitted through the acquisition zone 56. The
acquisition zone 56 can then be mapped onto paper having grids to
measure the top surface area of the acquisition zone 56.
The alternative method comprises mapping the density profile of the
absorbent member 42 to determine the top surface area of the
acquisition zone 56. The absorbent member 42 is cut into samples
having small areas. The density and basis weight of each of the
samples are then calculated using the techniques discussed above.
Thus, the relatively lower density and lower basis weight samples
are charted against the relatively higher density and higher basis
weight samples to measure the top surface area of the acquisition
zone 56.
The acquisition zone 56 can be of any desired shape consistent with
the absorbency requirements of the absorbent member 42 or diaper 20
including, for example, circular, rectangular, triangular,
trapezoidal, oblong, hourglass-shaped, funnel-shaped,
dog-bone-shaped or oval. Preferred shapes of the acquisition zone
56 are those that increase the perimeter of the interface between
the acquisition zone 56 and the storage zone 58 so that the
relative capillarity difference between the zones is fully
utilized. In a preferred embodiment, the acquisition zone will be
oval shaped having a top surface area of about 45 cm.sup.2 (about
7in.sup.2).
In order to maintain a certain minimal absorbency level in the
front section 50 of the absorbent member 42, the top surface area
or volume of the storage zone 58 must comprise some minimal amount
of the top surface area or volume of the front section 50. Thus, it
has been found that the acquisition zone 56 should preferably
comprise less than the entire top surface area and/or volume of the
front section 50 of the absorbent member 42. (Since in a preferred
embodiment the acquisition zone 56 is of generally uniform
thickness and cross-sectional area, volume can be interchanged with
top surface area as a definitional point.) The top surface area of
the portion of the acquisition zone 56 positioned in the front
section 50 of the absorbent member 42 preferably comprises less
than about 50% of the top surface area of the front section 50.
More preferably, the top surface area of the acquisition zone 56
comprises less than about 35% of the top surface area of the front
section 50 of the absorbent member 42, with less than about 20%
being especially preferred. In addition, the top surface area of
the acquisition zone 56 preferably comprises less than about 50% of
the top surface area of the deposition region 54, more preferably
less than about 35%, and most preferably less than about 20%.
The acquisition zone 56 may also have a number of different
cross-sectional areas and configurations including those wherein
the area of portions of the acquisition zone 56 is less or greater
than its top surface area (i.e., The acquisition zone 56 is smaller
or wider below the top surface of the absorbent member 42.) For
example, the acquisition zone 56 may have conical, trapezoidal,
T-shaped or rectangular cross-sectional areas. As shown in FIGS. 2
and 3, the acquisition zone 56 preferably has a rectangular
cross-sectional area so as to provide a uniform acquisition zone
56.
In addition, the acquisition zone 56 need not comprise the entire
thickness of the absorbent member 42, but may extend through only a
fraction of its total thickness. The acquisition zone 56 may also
have a different thickness than the surrounding storage zone 58.
However, in a preferred embodiment as shown in FIGS. 2 and 3, the
acquisition zone 56 preferably extends through the entire thickness
of the absorbent member 42 and has a thickness equal to the
thickness of the surrounding storage zone 58 in the deposition
region 54.
While the acquisition zone 56 may be transversely positioned
anywhere along the absorbent member 42, it has been found that the
acquisition zone 56 functions the most efficiently when it is
transversely centered within the front section 50 or the deposition
region 54 of the absorbent member 42. Thus, the acquisition zone 56
is preferably centered about the longitudinal centerline 68 of the
absorbent member 42. More preferably, the acquisition zone 56 is
transversely positioned only in the central region 64 of the front
section 50 or deposition region 54 of the absorbent member 42 such
that none of the acquisition zone 56 is located in the ear regions
60 and 62.
Such an absorbent member 42 is preferably made by airlaying a
thickness profiled absorbent member-preform and then calendering
the absorbent member 42 in a fixed-gap calender roll to effect
densifying the absorbent member 42. The thickness profiled
absorbent member 42 initially has areas of higher basis weight
which define the storage zone 58 and of lower basis weight which
define the acquisition zone 56. The absorbent member 42 is then
calendered preferably to at least a uniform thickness in the
deposition region. Thus, a lower average density and a lower
average basis weight per unit area acquisition zone 56 is created
relative to the higher average density and higher average basis
weight storage zone 58. Additionally, discrete particles of
absorbent gelling material are added to an air-entrained stream of
fibers prior to their deposition onto the preform to affect uniform
distribution of absorbent gelling material throughout the preformed
absorbent member 42. Thus, the resultant absorbent member 42
contains a uniform mixture of hydrophilic fibrous material and
discrete particles of absorbent gelling material.
In use, the diaper 20 is applied to a wearer, by positioning the
back waistband region 24 under the wearer's back, and drawing the
remainder of the diaper 20 between the wearer's legs so that the
front waistband region 22 is positioned across the front of the
wearer. The ends of the tape-tab fasteners 46 are then secured
preferably to outwardly facing areas of the diaper 20. In use,
disposable diapers or other absorbent articles having such
absorbent members 42 having a relatively lower average density and
lower average basis weight acquisition zone 56, tends to more
quickly acquire liquids into the acquisition zone 56 and to
distribute these liquids to the remaining portions of the absorbent
member 42 and to remain dry or dryer due to the preferential
capillarity between the storage zone and the acquisition zone 56 of
the absorbent member 42. Thus, such an absorbent member 42 helps to
alleviate leakage around the edges of such absorbent articles.
FIG. 5 shows an alternative embodiment of an absorbent member 542
of the present invention. As shown in FIG. 5, the front section 550
of the absorbent member 542 has a thickness, T1, greater than the
thickness, T2, of the back section 548. The acquisition zone 56 is
preferably of the same thickness, T1, as the storage zone 58
positioned in the front section 550 of the absorbent member 542;
the front section 550 having a terraced character by virtue of the
thickness difference between the front section 550 and the back
section 548 and by virtue of the relatively steep slope formed by a
density/basis weight transition zone which is designated 572.
Preferably, T1 is at least about 1.5 times as great as T2 and
preferably about 2.0 times as great as T2. In this preferred
embodiment, about three-fourths of the absorbent material is
disposed in the front section 550 of the absorbent member 542
thereby providing an absorbent member 542 wherein the front section
552 has high absorbent capacity as well as rapid acquisition
characteristics.
FIGS. 6 and 7 show a further alternative embodiment of an absorbent
member 642 of the present invention. An absorbent acquisition core
674 is positioned over the absorbent member 642 of the present
invention to form a dual-layer absorbent core. An example of a
similar dual-layer absorbent core is discussed in more detail in
United States patent application Ser. No. 734,426 filed by Paul T.
Weisman, Dawn I. Houghton, and Dale A. Gellert on May 15, 1985,
which is incorporated herein by reference.
The absorbent acquisition core 674 preferably consists essentially
of hydrophilic fibrous material. This absorbent acquisition core
674 thus serves to quickly collect and temporarily hold discharged
liquids and to transport such liquids by wicking from the point of
initial contact to other parts of the absorbent acquisition core
674. Since the primary function of the absorbent acquisition core
674 is to receive liquids passing through the topsheet 38 and to
transport such liquids to other areas of the absorbent acquisition
core 674 and eventually onto the absorbent member 642, the
absorbent acquisition core 674 can be substantially free of
absorbent gelling material. Alternatively, the absorbent
acquisition core 674 can contain particular amounts of absorbent
gelling material. Thus, the absorbent acquisition core 674, for
example, can contain up to about 50%, or preferably up to about 25%
or 40%, by its weight of particles of absorbent gelling material.
In the most preferred embodiments, the absorbent acquisition core
contains up to about 8% by its weight of particles of absorbent
gelling material. In some instances, the presence of particles of
absorbent gelling material in the absorbent acquisition core 674
can actually serve to maintain its density within the optimum range
to promote fluid distribution. The specific type of absorbent
gelling material optionally used in the absorbent acquisition core
674 does not have to be the same as the type essentially employed
in the absorbent member 642.
The shape, size and character, including capillarity of the
absorbent acquisition core 674, is of some importance in
determining the effectiveness of the resulting diaper 20 or other
absorbent article. The absorbent acquisition core 674 in the
unfolded configuration can be of any desired shape, for example,
rectangular, oval, oblong, asymmetric or hourglass-shaped. The
shape of the absorbent acquisition core 674 will frequently define
the general shape of the resulting diaper 20. In preferred
embodiments of the present invention as shown in FIG. 6, the
absorbent acquisition core 674 will be hourglass-shaped and will be
of a substantially uniform density within the range of from about
0.07 to about 0.20 g/cm.sup.3. Preferably, the core will have a
basis weight ranging from about 0.007 to about 0.075
g/cm.sup.2.
The absorbent acquisition core 674 may alternatively comprise a
core acquisition zone (not shown) having a lower average density
and a lower average basis weight than the remainder of the
absorbent acquisition core 674. This core acquisition zone may have
the same shape, positioning and characteristics as the acquisition
zone 656 of the absorbent member 642, or it may have different
shapes, positioning and/or characteristics. Preferably, the core
acquisition zone of the absorbent acquisition core 674 overlays at
least a portion of the acquisition zone 656 of the absorbent member
642, and more preferably the entire acquisition zone 656 of the
absorbent member 642, so as to provide an overall acquisition zone
extending throughout the entire thickness of the dual-layer
absorbent core system.
The absorbent member 642 of the present invention need not be as
large as the absorbent acquisition core 674 and can, in fact, have
a top surface area which is substantially smaller than the top
surface area of the absorbent acquisition core 674. Generally, the
absorbent member 674 will have a top surface area from about 0.25
to about 1.0 times that of the absorbent acquisition core 674. Most
preferably, the top surface area of the absorbent member 642 will
be only from about 0.25 to about 0.75, and most preferably from
about 0.3 to about 0.5, times that of the absorbent acquisition
core 674.
The absorbent member 642 is preferably placed in a specific
positional relationship with respect to the backsheet 40 and/or the
absorbent acquisition core 674 in the diaper or other absorbent
article. More particularly, the absorbent member 642 is positioned
generally toward the front of the diaper so that absorbent gelling
material is most effectively located to acquire and hold discharged
liquids from the absorbent acquisition core 674.
The forward postioning of the absorbent member 642 can be defined
by specifying the percent of total absorbent gelling material which
is found forward of particular points along the length of the
diaper or other absorbent article. Thus, in accordance with the
present invention, the absorbent member 642 is positioned relative
to the backsheet and/or the absorbent acquisition core such that
(1) at least about 75% of the total absorbent gelling material in
the absorbent member 642 is found within the front two-thirds
portion of the diaper or other absorbent article, and (2) at least
about 55% of the total absorbent gelling material in the absorbent
member 642 is found within the front half portion of the diaper or
other absorbent article. More preferably, the absorbent member 642
is positioned relative to the backsheet 38 and/or the absorbent
acquisition core 674 such that at least about 90% of the total
absorbent gelling material in the absorbent member 642 is found in
the front two-thirds portion and at least about 60% of the total
absorbent gelling material is found in the front half portion of
the diaper or other absorbent article. (As noted, for purposes of
the present invention, "portions" of the diaper or other absorbent
article can be defined by reference to the top surface area of the
unfolded diaper 20 or absorbent article found in front of a given
point on the line which defines the length of the diaper 20 or
absorbent article).
In the usual instance when the absorbent acquisition core 674
generally defines the shape of the diaper or other absorbent
article, the normal length of the backsheet 38 will be approached
by the longest longitudinal dimension of the absorbent acquisition
core 674. In such instances, the positioning of the absorbent
member 642 can also be defined with respect to its location toward
the front portion of the absorbent acquisition core 674. However,
in some applications (e.g. adult incontinence articles) wherein
bulk reduction or minimum cost are important, the absorbent
acquisition core would not take on the general shape of the diaper
or incontinence structure. Rather, it would be generally located to
cover only the gential region of the wearer and could in this case
have approximately the same top surface area as the absorbent
member 642. In this instance, both the absorbent acquisition core
674 and the co-extensive absorbent member 642 would be located
toward the front of the article as defined by only the backsheet 38
such that the requisite percentages of absorbent gelling material
would be found in the front two-thirds and front half sections
respectively of the diaper or other absorbent article.
The absorbent member 642 of the dual-layer absorbent core can be of
any desired shape consistent with comfortable fit including, for
example, circular, rectangular, trapezoidal, oblong,
hourglass-shaped, dog-bone-shaped or oval. If desired, the
absorbent member 642 can be wrapped in a high wet strength envelope
web such as tissue paper or a synthetic fine pore, e.g., nonwoven
material, to minimize the potential for particles of absorbent
gelling material to migrate out of the absorbent member 642.
Another objective of such overwrapping is to desirably increase the
in-use integrity of the dual layer absorbent core. Such a web can,
in fact, be glued to the absorbent member 642. Suitable means for
carrying out this gluing operation include the glue spraying
procedure described in U.S. Pat. No. 4,573,986 issued to Minetola
and Tucker, on Mar. 4, 1986, which patent is incorporated herein by
reference.
In preferred embodiments, the absorbent member 642 of the dual
layer absorbent core will be oblong. In especially preferred
embodiments, an oblong absorbent member 642 overwrapped with
spray-glued tissue will be employed.
Because the absorbent member 642 of the dual-layer absorbent core
is generally smaller than the absorbent acquisition core 674 such
that the absorbent member 642 may entirely be placed in the area of
typical liquid deposition, and because the absorbent member 642 is
preferably positioned in a specific positional relationship with
respect to the backsheet 38 and/or the absorbent acquisition core
674, the acquisition zone 656 may be positioned anywhere in the
absorbent member 642. The acquisition zone 656 is not necessarily
limited to a portion of the deposition region, since in effect the
entire absorbent member 642 of the dual-layer absorbent core is in
the "deposition region". The acquisition zone 656 is, however,
preferably positioned in a specific positional relationship with
respect to the backsheet 38 and/or the absorbent acquisition core
674 of the diaper or other absorbent article. More particularly,
the acquisition zone 656 should be positioned generally toward the
front of the diaper at least partially in the crotch region 26 so
that the acquisition zone 656 is most effectively located to
quickly acquire and distribute liquids within the absorbent member
642. Thus, the positioning of the acquisition zone 656 in the
diaper or other absorbent article can be defined by specifying the
percentage of the top surface area (and/or volume) which is found
forward of a particular point along the length of the diaper or
other absorbent article. In accordance with the present invention,
the acquisition zone 656 is preferably positioned relative to the
backsheet 38 and/or the absorbent acquisition core 674 such that
the top surface area of the acquistion zone 656 is completely
positioned within the front two-thirds portion of the diaper or
absorbent article. More preferably, the acquisition zone 656 is
positioned relative to the backsheet 38 and/or the absorbent
acquisition core 674 such that the top surface area of the
acquisition zone 656 is completely positioned within the front half
portion of the diaper or absorbent article and, most preferably,
such that at least about 30% of the top surface area is located in
the front one-third section of the diaper or absorbent article. The
acquisition zone 656 is also most preferably completely positioned
within the crotch region 26 of the diaper or absorbent article.
In order to maintain a certain minimal absorbency level in the
front portions of the diaper or other absorbent article, it has
been found that the top surface area of the acquisition zone 656
should comprise less than the entire top surface area of the
absorbent member 642 of the dual-layer absorbent core. The top
surface area (and/or volume) of the acquisition zone 656 preferably
comprises less than about 50% of the top surface area (and/or
volume) of the absorbent member 642. More preferably, the top
surface area of the acquisition zone 656 comprises less than about
35% of the top surface area of the absorbent member 642 and most
preferably less than about 20% of the top surface area of the
absorbent member 642. All other aspects of the acquisition zone 656
may be similar to the acquisition zone 56 discussed with respect to
the absorbent member 42.
FIG. 8 shows a still further alternative embodiment of an absorbent
member 842 of the present invention. The absorbent member 842 has
an asymmetric shape (i.e., the absorbent member 842 is not
symmetrical about its transverse centerline). In addition, the ear
regions 860 and 862 and the ear regions of the back section 848
preferably have a different thickness than the central region 864.
Further, the density and basis weight values of the ear regions 860
and 862 and the back section 848 are different from the storage
zone 858 positioned in the central region 864 by virtue of the
method by which the absorbent member 842 is formed.
The ear regions 860 and 862 and the back section 848 are preferably
formed with a lesser basis weight than the storage zone 858 of the
central region 864 so as to hold down the cost of such absorbent
members 842 because less materials are being used. The absorbent
member 842 is calendered to a uniform thickness in the central
region 864 and the back section 848 except for its ear regions; the
storage zone 858 of the central region 864, therefore, having a
greater average density than the back section 848 except for its
ear regions. (It should be understood that all or portions of the
back section 848 may alternatively be calendered to a lesser
thickness than the central region 864 such that the back section
848 has about an equal or a greater average density than the
storage zone 858.) The ear regions 860 and 862 and the ear regions
of the back section 848 are preferably calendered such that they
have substantially less thickness than the central region 864 and a
greater average density than the storage zone 858 of the central
region 864. The thickness difference between the ear regions and
the central region 864 is such that the absorbent member 842 may be
easily folded to a thin configuration during packaging with the ear
regions overlaying the respective central region 864 and the back
section 848. The ear regions are also preferably more dense than
the storage zone 858 to provide an additional capillarity
difference so that liquids will tend to be pulled toward the ear
regions so that the total absorbent capacity of the absorbent
member 842 will be utilized.
The acquisition zone 856 of the absorbent member 842 has a funnel
shape. The funnel shape is defined by a generally triangular
portion 884 in combination with a stem or rectangular portion 886.
The triangular portion 884 is especially effective in absorbing
liquids discharged by a male wearer, while the stem portion 886 is
effective for a female wearer. While it is possible that the shape
of the acquisition zone 856 may vary according to the type of
wearer contemplated, such as only a triangular portion 884 for a
male wearer and only a stem portion 886 for a female wearer, it is
preferred that the acquisition zone 856 comprise both elements.
Yet another alternative to each of the embodiments of the above
absorbent members of the present invention comprises varying the
pore size of the fibers without necessarily varying the density of
the fibers to form an acquisition zone and a storage zone. For
example, fine fiber dimensions of hardwood fluff can be utilized to
advantage by substituting at least about 50%, and preferably about
80% to 100%, hardwood fluff fibers of approximately the same
density as lower density softwood fluff fibers for the softwood
fibers in the storage zone. This can be done because the hardwood
fluff has a smaller pore size than the softwood fluff material. As
result, a capillarity difference will still be obtained within the
scope of the invention, even if the density of each zone is the
same. Thus, for example, an absorbent member can be obtained from
using a predominately softwood pulp with a fine pore structure to
define the acquisition zone and a predominately hardwood fluff pulp
to define the storage zone.
While particular embodiments of the present invention have been
illustrated and described, it would be obvious to those skilled in
the art that various other changes and modifications can be made
without departing from the spirit and scope of the invention. It is
therefore intended to cover in the appended claims all such changes
and modifications that are within the scope of this invention.
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